(ITS#3445) HEAD fails to build on Windows (zn_malloc)

Full_Name: Howard Chu
Version: HEAD
OS: Windows XP
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (194.230.238.25)
Submitted by: hyc
The file slapd/zn_malloc.c includes <sys/mman.h> and uses mmap/munmap system
calls unconditionally. There needs to be a configure test for their presence and
#ifdef's around their usage. Some reasonable behavior needs to be present for
platforms where these functions don't exist...